The visual control of locomotion is based on the detection of Optical flow patterns produced at a moving point of observation. This project would continue research on the perception of heading from optical flow and extend this research by examining the functional significance of optical flow for the control of gait and posture during walking. One set of perceptual experiments will address outstanding questions regarding: (1) the effects of surface texture, shading, 3D structure, and flow field noise on the perception of heading, (2) the importance of specific flow field variables for perception of translational and curvilinear heading, and (3) the decomposition of eye rotation during translation and during curvilinear movement. A second set of perceptual-motor experiments will attempt to map out directionally-specific, phase-dependent control relations between optical flow variables and the motor parameters of gait and posture. Subject will view large-field optical flow displays projected in a hemispherical dome during treadmill walking, while their gait kinematics and dynamics are monitored. The control relations will be tested using four types of manipulations: (1) sudden perturbations of the optical flow field that induce adjustments in gait, (2) continuous oscillations in the flow field that induce postural sway during walking, (3) qualitative changes from one class of optical flow patterns to another, e.g. translational to curvilinear movement, and (4) rearrangement of the relationship between the optical flow pattern and the gait effectors. The results will contribute to basic knowledge about the visual control of locomotion, and will provide a basis for understanding perceptual-motor and gait disorders.